Ethusa pygmaea Alcock, 1894

Castro, Peter, 2005, Crabs of the subfamily Ethusinae Guinot, 1977 (Crustacea, Decapoda, Brachyura, Dorippidae) of the Indo-West Pacific region, Zoosystema 27 (3), pp. 499-600 : 541-542

Ethusa pygmaea Alcock, 1894

Ethusa pygmaea Alcock, 1894: 406 ; 1896: 284; 1899: 33. — Doflein 1904: 291 (list), fig. 64. — Chen 1993: 318 (key), 333, fig. 13.

Aethusa pygmaea – Alcock & Anderson 1895: pl. 14, fig. 5.

Ethusa pygmea [sic] – Serène 1968: 40 (list). — Serène & Lohavanijaya 1973: 34 (key).

Not Ethusa pygmaea – Ihle 1916b: 141, 151 (list), 153 (list), 156 (list) (= E. longidentata Chen, 1997 ?).

TYPE MATERIAL. — Unknown (Zoological Survey of India, Calcutta?).

TYPE LOCALITY. — India, Andaman Islands.

MATERIAL EXAMINED. — New Caledonia. BIOCAL, stn DW 33, 23°10’S, 167°10’E, 675-680 m, 29.VIII.1985, 1 juv. ( MNHN-B 18402).

MUSORSTOM 4, stn DW 197, 18°51.3’S, 163°21.0’E, 650 m, 20.IX.1985, 1 ( MNHN-B 18420).

CHALCAL 2, stn DW 74, 24°40.36’S, 168°38.38’E, 650 m, 29.X.1986, 1 (MNHN-B 19090), 1, 1 ovig. (MNHN-B 19091). — Stn DW 75, 24°39.31’S, 168°39.67’E, 600 m, 29.X.1986, 1, 2 ovig. (MNHN-B 19089).

NORFOLK 1, stn DW 1700, 24°40’S, 168°40’E, 572-605 m, 24.VI.2001, 1 (MNHN-B 28554).

DISTRIBUTION. — Andaman Is ( Alcock 1894), New Caledonia ( Chen 1993). Depth: 155 ( Alcock 1896) - 680 m ( Fig. 34 ).

SIZE. — Maximum size: cl 5.7 mm, cw 5.3 mm (MNHN-B 19089), cl 8.9 mm, cw 8.7 mm (MNHN-B 18420).

REMARKS

Material collected from New Caledonia agrees with the description and illustration of Ethusa pygmaea Alcock, 1894 ( Alcock 1894: 406; Alcock & Anderson 1895: pl. 14, fig. 5) and particularly with specimens previously identified as such by Chen (1993: fig. 13). Unfortunately, the type material could not be located.

The Siboga material identified by Ihle (1916a) does not agree with Alcock’s description or with the New Caledonia specimens. It is very close and most probably conspecific to E. longidentata Chen, 1997 (see above).

Other than its small size, diagnostic to this species are outer orbital teeth that are relatively slender, directed outwardly, and shorter than the frontal teeth ( Alcock & Anderson 1895: pl. 14, fig. 5; Chen 1993: fig. 13a, b). The two portions of the anterior border proximal to the frontal teeth are swollen, as evidenced by the distended inner side of each orbital sinus. The anterior border of the endostome just reaches the proximal edge of the antennular fossae of the basal antennular articles. Alcock (1894: 406) describes the carapace and pereopods as “finely and closely granular”. These characters, however, are also present in E. parapygmaea Chen, 1993 . The only reliable way of differentiating between these two species are their G1 (see Remarks of E. parapygmaea above). Only the examination of the type material of E. pygmaea may show if the Western Pacific specimens described here actually belong to Alcock’s species.

The granulation of the pereopods, which was given as a difference between E. pygmaea and E. indica Alcock, 1894 , was observed in the New Caledonia specimens. Also noticeable is the “better definition of the regions of the carapace” in E. pygmaea . A more noticeable difference is the shape of the outer orbital teeth: very slender and typically outwardly projecting in E. indica ( Alcock & Anderson 1895: pl. 14, fig. 2) in contrast to slightly widened at the base, hence slightly triangular, in E. pygmaea ( Alcock & Anderson 1895: pl. 14, fig. 5). The P4 and P5 are described by Alcock (1894: 406) as “more robust” in E. pygmaea than in E. indica . This difference, however, is not evident in the illustrations or in the actual specimens. Furthermore, their G1 are different and the meri of P2 and P3 are relatively longer in E. indica than in E. pygmaea . These differences and the presence of ovigerous females preclude the possibility that E. pygmaea actually represents the juvenile stage of E. indica .

Figures

FIG. 34. — Bathymetric distribution of Indo-West Pacific ethusine crabs.